Feedback from Perlite/Cement oven owners?

[Gulf]

Hi Jcamozzi, Welcome to the forum. If you haven't already, read through several more of the builds in this sub-forum. Other Oven Types. Some of these members may not still be following the forum. You may try tagging or messaging them direct if you don't get responses to your question inside this particular thread.

[jcamozzi]

Can anyone let me know if you built a Perlite/Cement oven how has it held up? Would you recommend building one? Looking to see what options I have. I'm in the planning stages. Thanks!

[peatsatime]

Ok. Last question. Would lining the inside of the oven with very thin gauge stainless steel be an option? Would that at least keep out the nasty stuff from falling onto the food? If I could get 3-6 months of use out of this build I wouldnt be as pissed. The next oven will be done with much more research and with fire brick . Thanks so much and sorry for all the noob questions

If you are able to flip it upside down, you can try what I did. I used castable refractory cement from home depot and put 1/2" layer inside the dome. I've brought it up to full temp a dozen or so times and it's holding up so far. Any areas that did not have it just disintegrated, so went back and covered those as well.

I am another victim of all the diy info out there for casting. Unfortunately I found this forum far too late after i finished my build, but I will say so far it's been working out great. Knowing what I know now, I would have gone a different direction I think. I'll make a thread on mine at some point, but it's the infamous inflatable ball method as well...lol.

[david s]

Forming against a compound curve with flat stainless would be a challenge.

[Brando23]

Ok. Last question. Would lining the inside of the oven with very thin gauge stainless steel be an option? Would that at least keep out the nasty stuff from falling onto the food? If I could get 3-6 months of use out of this build I wouldnt be as pissed. The next oven will be done with much more research and with fire brick . Thanks so much and sorry for all the noob questions

[david s]

Clay/sand contains no cementious material and if applied in a thin layer is more likely to crack and flake off, IMO, especially because you are increasing the proportion of clay which shrinks.

[Brando23]

Thank you for the prompt reply and advise. I attached some photos. I have not fired the oven yet. The first two weeks it was covered with a damp bed sheet. It was uncovered for two weeks, removed the yoga ball and then I applied the fireclay outer layer. I can get to the interior fairly easily to apply a layer over the perlite. Would a clay/sand mixture be an option ?

[david s]

Hi Brando,
it sounds like you have already dried and fired the oven in which case adding a layer to the inside will be difficult. Not only will it be hard to get in there and apply it, there are problems with bonding onto a dry surface. The surface should be damp, but not wet, so there is a reduced suction of water from the material applied to it. If the water is sucked out of the material being applied there will not be enough for the chemical process of hydration to take place. Additionally, the material will require extended damp curing for at least a week in the case of Portland cement and a min of 24 hrs for CAC. This maybe difficult if not impossible for you to achieve. Also any thin layer is more likely to be more vulnerable to cracking and flaking. After the operation the oven will have to be slowly dried again or the sudden water removal can create problems. By all means give it a go, you may be successfu, but I wouldn’t be too hopeful. Good luck.
Dave

[Brando23]

Hello, I also fell into the "quick and easy" perlite oven on YouTube. Basically I did more research during the build and realized that a lot of these perlite ovens are not very durable or even safe. I am trying to salvage the project though and i made a home brew fireclay cement to cover the top of the perlite cement mold and too fix a crack . Now I would like to apply something to the inside of the oven so that the perlite/cement doesn't get into our food. Would the 3:1:1:1 home brew work ? Or a store bought high heat refractory cement ? thanks for the advise

[CoastalPizza]

...Did you have any issues with those small holes on the dome after several fires?...

No, none at all. They are only 1/4" (6 mm) diameter — I just covered them with the rockwool batt insulation which was then covered in ~2" (50 mm) of perlcrete and then the render coat so they are fully blocked off from the outside.

[mkasap]

Good morning David. If my oven is going to have a total weight of around 350kg then most probably i will make second thoughts for the portable version as my backyard is mainly grass which will make the oven’s portability a nightmare. It’s sad because i collected all the materials needed and i wanted to start the construction now instead of waiting till we move to the new house. But seeing that a portable version won’t be really portable, unfortunately i have to wait till the end of November.

[david s]

Firstly it is more expensive to fabricate a steel stand and fit it with wheels. Moving the oven should not be a problem regards cracking although it is with a trailerable version. You do need to make sure the wheels are at least 100 mm diam (small wheels risk getting jammed and creating a dangerous capsize with around 350 kg falling about a metre), two of them swivelers and lockable (all these wheels have a load rating that shouldn’t be exceeded). Forget trying to move it over rough surfaces or grass. The first steel stand I built was of 25 mm square rolled hollow section, but a fairly thin grade ( 1.2 mm from memory. It seemed plenty strong enough until I mounted the oven on it. I thought it had too much flex, but it still stands and is operating some nine years later without problems. I now use and recommend 4 mm thick 50 x 50 mm galvanised angle, which is much stronger. It is really far easier, stronger, safer and cheaper to build a masonry stand. The downside is that the oven can’t be moved.

Regarding the chicken wire, it won’t do much good in the vermicrete layer but would be useful over the top of it so the outer rendered shell will be reinforced by it. I gave up with this method years ago as it is quite time consuming. I now simply add random reinforcing fibres into the outer render when mixing.

[mkasap]

david s May i have your feedback please, regarding making my oven portable? Thank you.

Thank you very much for your long informative reply, that’s exactly the reason why i’ve asked you specifically. Im taking your suggestions very seriously because after the perlcrete catastrophe i want to build something long-lasting but also eliminate any possible sources of contamination. My chicken wire is indeed very thin but i’m not gonna risk it because i can’t be sure that i will install it under the inner surface all over so, it’s rejected. I will only use it in the insulation layer. Another concern i have is regarding making my oven portable. I want to create a metal base approx. 140x90x90cm (LxWxH) to build my oven on, with four heavy duty wheels. Do you think my oven will suffer from vibrations from moving it around the house, increasing the risk of cracking? Thanks again and im sorry for bombarding you with all these questions.

[mkasap]

Thank you very much CoastalPizza. Your oven looks rock solid - well done!! Did you have any issues with those small holes on the dome after several fires? Photos are saved for future reference

[CoastalPizza]

...create a vertical mould for the first 20-30cm of the dome and after 2-3 days continue building the rest of the dome based on the sand mould....

This is exactly how I built mine - see the build thread link.
Post #4 shows the finished ring mold
Post #9 shows the cast ring after the mold is removed
Post #10 shows the sand filling the ring and the casting of the domed top
The casting was done using the 3:1:1:1 formula home-brew that David S recommends with about 2% by weight stainless steel needles added.